The “special relationship” between the US and the UK lay in tatters on Wednesday after the resignation of Kim Darroch as the British ambassador to Washington.

“The current situation is making it impossible for me to carry out my role as I would like,” he announced.

Darroch’s days were numbered ever since his confidential reports to London, describing the Trump administration as “inept” and “dysfunctional”, were leaked to the Mail on Sunday. On Tuesday he was “disinvited” to a White House dinner for the visiting Emir of Qatar.

The Prime Minister Theresa May said his departure was “a matter of deep regret”.

She told the Commons: “I hope this House will reflect on the importance of defending our values and principles particularly when they are under pressure.”

Darroch’s resignation is not entirely unexpected after President Donald Trump had announced that “we will no longer deal with him” and described the career diplomat in further tweets as “wacky”, “a very stupid guy” and a “pompous fool”.

However, the timing of his resignation appears linked to Boris Johnson’s failure to give him unqualified support when the former appeared in a head to head live debate with the foreign secretary Jeremy Hunt on ITV on Tuesday evening.

The Mirror, a Labour supporting tabloid, went for Boris’s jugular in its front page headline on Wednesday: “Traitor Boris backs Trump Not Britain.”

Even The Times, which is backing Boris for Prime Minister, was critical in its page one headline of his failure to be more robust in supporting the British ambassador: “Johnson raises pressure on besieged ambassador.”

It has been reported that Darroch submitted his resignation to Simon McDonald, the civil servant who is head of the foreign & commonwealth office as its permanent undersecretary ( the equivalent of India’s foreign secretary), after watching Johnson in the live debate.

Darroch said in his resignation letter: “Since the leak of official documents from this embassy there has been a great deal of speculation surrounding my position and the duration of my remaining term as ambassador.

“I want to put an end to that speculation. The current situation is making it impossible for me to carry out my role as I would like.

“Although my posting is not due to end until the end of this year, I believe in the current circumstances the responsible course is to allow the appointment of a new ambassador.”

He added he was “grateful” to those in the UK and the US who have offered him support during what he has described as these “difficult few days”.

He went on: “This has brought home to me the depth of friendship and close ties between our two countries. I have been deeply touched.”

Boris inevitably faced a backlash amid claims from foreign office minister Alan Duncan and others that he hung Darroch out to dry by refusing to rule out sacking him during the TV debate.

Duncan said Boris had “basically thrown this fantastic diplomat under the bus to serve his own personal interests”.

He called Boris, his former boss, an “utter wimp” after he failed to guarantee the diplomat’s future: “Am severely disappointed that Boris Johnson appears unwilling to stand up for our ambassador to the US, our PM or our country. What does that tell you? Utter wimp when the crunch comes when he should be making a stand. Err... next PM??”

Labour branded Boris a “pathetic lickspittle” who had bowed to Trump’s “tantrums”, while former foreign secretary David Miliband said he was “spineless”.

Boris tried to defuse the crisis by insisting he “regretted” Darroch’s decision to resign.

“He is a superb diplomat,” said Johnson. “I worked with him for many years. Whoever leaked his DipTels (diplomatic telegrams) has done a great disservice. I hope whoever did is run down and caught and eviscerated, quite frankly. It is not right that civil servants’ careers should be dragged into the political agenda.”

In his reply McDonald said he was accepting the ambassador’s resignation with “deep personal regret”.

“Over the last few difficult days you have behaved as you have always behaved over a long and distinguished career, with dignity, professionalism and class,” he said.

“The Prime Minister, Foreign Secretary and whole of the public service have stood with you: you were the target of a malicious leak; you were simply doing your job. I understand your wish to relieve the pressure on your family and your colleagues at the embassy; I admire the fact that you think more of others than yourself. You demonstrate the essence of the values of British public service.”

Hunt said in an official statement: “If one theme ran through all his endeavours, it was his unswerving devotion to upholding the interests of the United Kingdom, in the best tradition of British diplomacy.

“In that spirit, he brought dispassionate insight and directness to his reporting to ministers in London. Whenever I visited Washington as Foreign Secretary, I was struck by Sir Kim’s professionalism and intellect. I am outraged that a selection of his reports should have been leaked.

“I am sure that our Ambassadors worldwide will continue to provide the objective and rigorous reporting that the Foreign and Commonwealth Office has always prized. I profoundly regret how this episode has led Sir Kim to decide to resign.”

There was speculation that Boris may not retain Hunt as foreign secretary.